The present invention relates to a radar system having means for producing a code, means for modulating a transmission signal in a transmit branch using the code, means for delaying the code, means for modulating a signal in a receive branch using the delayed code, and means for mixing a reference signal with a receiving signal. The present invention also relates to a method for coding a radar system having the steps: generating a code, modulating a transmission signal in a transmit branch using the code, delaying the code, modulating a signal in a receive branch using the delayed code, and mixing a reference signal with a receiving signal.
There are numerous applications for radar systems in the most varied fields of technology. For instance, it is possible to install radar sensors in motor vehicles for very short range sensor systems.
In radar systems, in principle, electromagnetic waves are radiated by a transmission antenna. If these electromagnetic waves hit an obstacle, they are reflected, and after the reflection they are received by another or by the same antenna. Thereafter, the received signals are supplied to a signal processing and a signal evaluation.
For example, in motor vehicles, radar sensors are installed for measuring the distance to targets and/or the relative speed with respect to such destinations outside the motor vehicle. As targets, for example, preceding or parking motor vehicles come into consideration.
FIG. 1 shows a schematic representation of a radar system having a correlation receiver representing the state of the art. A transmitter 300 is induced by pulse generation 302 to radiate a transmission signal 306 from an antenna 304. The transmission signal 306 hits a target object 308, where it is reflected. The receiving signal 310 is received by antenna 312. This antenna 312 may be identical to antenna 304. After receiving signal 310 is received by antenna 312, this is communicated to receiver 314, and subsequently, via a unit 316 having a lowpass filter and an analog-digital converter, is supplied to a signal evaluation 318. The specialty about the correlation receiver is that receiver 314 receives a reference signal 320 from pulse generation 302. Receiving signals 310 received by receiver 314 are mixed in the receiver 314 with reference signal 320. Because of the correlation, conclusions may be drawn, for instance, as to the distance of a target object, on the basis of the temporal delay between the transmitting and receiving of the radar impulses.
In principle, it is desirable to separate interference signals, which may, for instance, originate from other transmission antennas, from portions of the signal reflected from the targets. Interferences are produced, for example, by other radar sensors, transmitters, consumers on the vehicle electrical system of the motor vehicle, cellular phones or by noise. Methods are already known which use an additional modulation of signals to separate interference signals from signal portions reflected from the targets. Likewise, it has already been proposed to use pseudo-noise coding (PN coding) for suppressing interference signals. By this coding it is supposed to be achieved that such interferences are minimized, in particular, the signal/noise (S/N) ratio in the output signal of the radar system being supposed to be increased. By such an increase in the S/N ratio it is made possible either to detect targets having a lower reflecting cross section or to decrease the pulse peak performance at constant S/N. The advantages of detecting targets having a lower reflecting cross section are, for instance, that a motor vehicle not only detects a preceding motor vehicle, but also, with great probability, pedestrians and bicyclists. The decrease in pulse peak performance has the result that lesser interferences from other systems, such as from directional radio systems, are brought about; in this connection, the decrease in pulse peak performance simplifies the approval of sensors by the appropriate regulating authorities.
According to a first specific embodiment, the present invention builds up on the radar system of the related art in that the modulation of one of the signals is carried out by an amplitude modulation (ASK; xe2x80x9cAmplitude Shift Keyingxe2x80x9d), and the modulation of the other signal is carried out by a phase modulation (PSK; xe2x80x9cPhase Shift Keyingxe2x80x9d). In this manner, an improvement in the S/N ratio is achieved. Thereby targets having a clearly lower reflection cross section may be detected, than used to be possible with radar systems of the related art having pure BPSK (xe2x80x9cBinary Phase Shift Keyingxe2x80x9d) or amplitude modulation. It is also possible to lower the pulse peak performance at a constant S/N ratio.
In the first specific embodiment it is particularly advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been discussed comprehensively in the literature, so that the present invention, in using PN codes, can be especially well implemented.
Preferably, the modulation of transmitting signals in the first specific embodiment is carried out by amplitude modulation, and the modulation of the signal in the receive branch is done by phase modulation. By using an amplitude modulation ASK in the transmit branch, this results in an improvement of the S/N ratio as opposed to using pure phase modulation PSK. The average transmitting power drops off by ca 3 dB as opposed to a phase modulation PSK in the transmit branch.
Likewise, it may be preferred in the first specific embodiment that the modulation of the transmitting signal is done by phase modulation, and that the modulation of the signal in the receive branch is done by amplitude modulation.
The first specific embodiment is advantageous when the means for mixing the reference signal with the received signal emit an output signal at a lowpass filter. The output signal is integrated using the lowpass filter, so that a suitable signal for further processing is available.
In the first specific embodiment, digital means for controlling the delay are preferably provided. Such digital means, such as a microcontroller or a digital signal processor are in a position to delay both the pulse repetition rate and the P/N code in a suitable manner, so that the signals in the receive branch experience the required correlation.
But in the first specific embodiment it may also be advantageous if circuitry means are provided for controlling the delay. Besides controlling the delay using digital means, it is also possible to install hardware for implementing the delay.
In the first specific embodiment, preferably, the means for producing and delaying an n-bit PN code are implemented as n-bit counters having combinatorial linkage of the counter outputs. An n-bit shift register makes several outputs available, the same PN code being made available at each output having in each case different temporal delays. Thus it is possible, in a simple way, to make available any desired code delays by a corresponding combinatorial linkage of the weighted outputs.
In the first specific embodiment it may also be of advantage if the receive branch is subdivided into several channels which use several PN codes for modulating, and if several lowpass filters are provided for further processing of the modulated signals. Because of this, the radar system may be broadened to include the evaluation of other signals transmitted by other radar sensors and modulated using other PN codes.
In the first specific embodiment it is particularly advantageous if means for blanking of phase transitions are provided. Since the transition of the phase relation in the actual setup does not occur instantaneously, errors occur after the integration of the signal. However, if the phase-modulated signal is blanked during the transition time between the various phase relations, these errors may be minimized. In the case of a combination, according to the present invention, of an amplitude modulation and a phase modulation, the bandwidth of the amplitude spectrum becomes greater. This improves the separability of different targets at equal pulse repetition rate, a smaller increment, however, being required for shifting the PN code. Alternatively, the pulse width may also be increased at almost unchanged high-sensitivity resolution, separability, increment and bandwidth.
In the first specific embodiment, a means for blanking phase transitions has a means for pulse formation and a switch, the switch being positioned in series with a means for phase modulation. The sequence of the means for phase modulation and the switch is a matter of choice. It is also conceivable that the blanking might be located between the receiving antenna and the mixer, or between the mixer and the subsequent lowpass filter. The phase modulation may also be located between the receiving antenna and the mixer. A suitable temporal window for the blanking is generated by the pulse formation.
According to a second specific embodiment, the present invention builds up on the radar system of the related art by having the modulation of at least one of the signals take place by a phase modulation (PSK; xe2x80x9cPhase Shift Keyingxe2x80x9d), and by having means for blanking of phase transitions provided. Since the transition of the phase relation in the actual setup does not occur instantaneously, errors occur after the integration of the signal. However, if the phase-modulated signal is blanked during the transition time between the various phase relations, these errors may be minimized. In the case of a combination, according to the present invention, of an amplitude modulation and a phase modulation, the bandwidth of the amplitude spectrum becomes greater. This improves the separability of different targets at equal pulse repetition rate, a smaller increment, however, being required for shifting the PN code. Alternatively, the pulse width may also be increased at almost unchanged high-sensitivity resolution, separability, increment and bandwidth.
In the second specific embodiment of the radar system according to the present invention, it is particularly advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been discussed comprehensively in the literature, so that the present invention, in using PN codes, can be especially well implemented.
In the second specific embodiment, a means for blanking phase transitions preferably has a means for pulse formation and a switch, the switch being positioned in series with a means for phase modulation. The sequence of the means for phase modulation and the switch is optional. It is also conceivable that the blanking might be located between the receiving antenna and the mixer, or between the mixer and the subsequent lowpass filter. The phase modulation may also be located between the receiving antenna and the mixer. A suitable temporal window for the blanking is generated by the pulse formation.
Preferably, the modulation of transmitting signals in the second specific embodiment is carried out by amplitude modulation, and the modulation of the signal in the receive branch is done by phase modulation. By using an amplitude modulation ASK in the transmit branch, this results in an improvement of the S/N ratio as opposed to using pure phase modulation PSK. The average transmitting power drops off by ca 3 dB.
Likewise, it may be preferred in the second specific embodiment that the modulation of the transmitting signal is done by phase modulation, and that the modulation of the signal in the receive branch is done by amplitude modulation.
The second specific embodiment is advantageous when the means for mixing the reference signal with the received signal emit an output signal at a lowpass filter. The output signal is integrated using the lowpass filter, so that a suitable signal for further processing is available.
In the second specific embodiment, digital means for controlling the delay are preferably provided. Such digital means, such as a microcontroller or a digital signal processor are in a position to delay both the pulse repetition rate and the P/N code in a suitable manner, so that the signals in the receive branch experience the required correlation.
But in the second specific embodiment it may also be advantageous if circuitry means are provided for controlling the delay. Besides controlling the delay using digital means, it is also possible to install hardware for implementing the delay.
In the second specific embodiment, preferably, the means for producing and delaying an n-bit PN code are implemented as n-bit counters having combinatorial linkage of the counter outputs. An n-bit shift register makes several outputs available, the same PN code being made available at each output having in each case different temporal delays. Thus it is possible, in a simple way, to make available any desired code delays by a corresponding combinatorial linkage of the weighted outputs.
In the second specific embodiment it may also be of advantage if the receive branch is subdivided into several channels which use several PN codes for modulating, and if several lowpass filters are provided for further processing of the modulated signals. Because of this, the radar system may be broadened to include the evaluation of other signals transmitted by other radar sensors and modulated using other PN codes.
According to a first specific embodiment, the present invention builds up on the method of the related art in that the modulation of one of the signals is carried out by an amplitude modulation (ASK; xe2x80x9camplitude shift keyingxe2x80x9d), and the modulation of the other signal is carried out by a phase modulation (PSK; xe2x80x9cPhase Shift Keyingxe2x80x9d). In this manner, an improvement in the S/N ratio is achieved. Thereby targets having a clearly lower reflection cross section may be detected, than used to be possible with radar systems of the related art having pure amplitude modulation. It is also possible to lower the pulse peak performance at a constant S/N ratio.
In the first specific embodiment of the method the code is preferably a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been discussed comprehensively in the literature, so that the present invention, in using PN codes, can be especially well implemented.
Preferably, the modulation of transmitting signals, in the first specific embodiment of the method, is carried out by amplitude modulation, and the modulation of the signal in the receive branch is done by phase modulation. By using an amplitude modulation ASK in the transmit branch, this results in an improvement of the S/N ratio as opposed to using pure phase modulation PSK. The average transmitting power drops off by ca 3 dB.
Likewise, it may be advantageous, in the first specific embodiment of the method, that the modulation of the transmitting signal is done by phase modulation, and that the modulation of the signal in the receive branch is done by amplitude modulation.
Advantageously, in the first specific embodiment of the method, the mixed signal is output to a lowpass filter. The output signal is integrated using the lowpass filter, so that a suitable signal for further processing is available.
It is of advantage if, in the first specific embodiment of the method, the delay is digitally controlled. Digital means, such as a microcontroller or a digital signal processor are in a position to delay both the pulse repetition rate and the P/N code in a suitable manner, so that the signals in the receive branch experience the required correlation.
However, it may also be useful if, in the first specific embodiment of the method, the delay is controlled by circuitry means. Besides controlling the delay using digital means, it is also possible to install hardware for implementing the delay.
In the first specific embodiment of the method, preferably, an n-bit PN code is generated and delayed by an n-bit counter having combinatorial linkage of the counter outputs. An n-bit shift register makes several outputs available, the same PN code being made available at each output having in each case different temporal delays. Thus it is possible, in a simple way, to make available any desired code delays by a corresponding combinatorial linkage of the weighted outputs.
The present invention may be of special advantage if, in the first specific embodiment of the method, the receive branch is subdivided into several channels which use several PN codes for modulating, and if the modulated signals are processed further by several lowpass filters. Because of this, the radar system may be broadened to include the evaluation of other signals transmitted by other radar sensors and modulated using other PN codes.
It is particularly advantageous, in the first specific embodiment of the method, if the phase transitions are blanked. Since the switching of the phase relation in the actual setup does not occur instantaneously, errors occur after the integration of the signal. However, if the phase-modulated signal is blanked during the transition time between the various phase relations, these errors may be minimized. In the case of a combination, according to the present invention, of an amplitude modulation and a phase modulation, the bandwidth of the amplitude spectrum becomes greater. This improves the separability of different targets at equal pulse repetition rate, a smaller increment, however, being required for shifting the PN code. Alternatively, the pulse width may also be increased at almost unchanged high-sensitivity resolution, separability, increment and bandwidth.
The first specific embodiment of the method is especially advantageous because a means for blanking phase transitions has a means for pulse formation and a switch, the switch being positioned in series with a means for modulating. The sequence of the means for phase modulation and the switch is optional. It is also conceivable that the blanking might be located between the receiving antenna and the mixer, or between the mixer and the subsequent lowpass filter. The phase modulation may also be located between the receiving antenna and the mixer. A suitable temporal window for the blanking is generated by the pulse formation.
According to a second specific embodiment, the present invention builds up on the method of the related art by having the modulation of at least one of the signals take place by a phase modulation (PSK; xe2x80x9cPhase Shift Keyingxe2x80x9d), and by having means phase transitions blanked. Since the transition of the phase relation in the actual setup does not occur instantaneously, errors occur after the integration of the signal. However, if the phase-modulated signal is blanked during the transition time between the various phase relations, these errors may be minimized. In the case of a combination, according to the present invention, of an amplitude modulation and a phase modulation, the bandwidth of the amplitude spectrum becomes greater. This improves the separability of different targets at equal pulse repetition rate, a smaller increment, however, being required for shifting the PN code. Alternatively, the pulse width may also be increased at almost unchanged high-sensitivity resolution, separability, increment and bandwidth.
In the second specific embodiment of the system it is particularly advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been discussed comprehensively in the literature, so that the present invention, using as it does, PN codes, can be especially well implemented.
The second specific embodiment of the method is especially advantageous because a means for blanking phase transitions has a means for pulse formation and a switch, the switch being positioned in series with a means for modulating. The sequence of the means for phase modulation and the switch is optional. It is also conceivable that the blanking might be located between the receiving antenna and the mixer, or between the mixer and the subsequent lowpass filter. The phase modulation may also be located between the receiving antenna and the mixer. A suitable temporal window for the blanking is generated by the pulse formation.
Preferably, the modulation of transmitting signals, in the second specific embodiment of the method, is carried out by amplitude modulation, and the modulation of the signal in the receive branch is done by phase modulation. By using an amplitude modulation ASK in the transmit branch, this results in an improvement of the S/N ratio as opposed to using pure phase modulation PSK. The average transmitting power drops off by ca 3 dB.
Likewise, it may be advantageous, in the second specific embodiment of the method, that the modulation of the transmitting signal is done by phase modulation, and that the modulation of the signal in the receive branch is done by amplitude modulation.
Advantageously, in the second specific embodiment of the method, the mixed signal is output to a lowpass filter. The output signal of the mixer is integrated using the lowpass filter, so that a suitable signal for further processing is available.
It is of advantage if, in the second specific embodiment of the method, the delay is digitally controlled.
Digital means, such as a microcontroller or a digital signal processor are in a position to delay both the pulse repetition rate and the P/N code in a suitable manner, so that the signals in the receive branch experience the required correlation.
However, it may also be useful if, in the second specific embodiment of the method, the delay is controlled by circuitry means. Besides controlling the delay using digital means, it is also possible to install hardware for implementing the delay.
In the second specific embodiment of the method, preferably, an n-bit PN code is generated and delayed by an n-bit counter having combinatorial linkage of the counter outputs. An n-bit shift register makes several outputs available, the same PN code being made available at each output having in each case different temporal delays. Thus it is possible, in a simple way, to make available any desired code delays by a corresponding combinatorial linkage of the weighted outputs.
The second specific embodiment of the method may be of special advantage in that the receive branch is subdivided into several channels which use several PN codes for modulating, and in that the modulated signals are processed further by several lowpass filters. Because of this, the radar system may be broadened to include the evaluation of other signals transmitted by other radar sensors and modulated using other PN codes.
The present invention is based on the surprising realization that, by a combination of the amplitude modulation ASK and the phase modulation PSK an improvement of the S/N ratio as well as of the quality of target detection may be achieved. With the aid of blanking the phase transitions, errors caused by non-instantaneous switching of the phase transitions may be minimized. The use of discrete code shifting permits a linear blanking of the measured space. The accuracy of this blanking depends mainly on the accuracy of the pulse repetition rate, which can be set very accurately. The digital circuits for producing codes and for shifting codes, as well as the circuits and mixers may be well integrated, for example, in a xe2x80x9cmonolithic microwave integrated circuitxe2x80x9d (MMIC).